A variety of biochemical events, particularly changes in ion transport, protein synthesis and the like are involved in the repair of fractured bones. It has long been recognized that properly applied electro-therapy signals can stimulate bone growth in the vicinity of fresh fractures and non-union fractures, and apparently do so by initiating or stimulating the requisite biochemical changes. Extensive research has been conducted in both experimental animal studies and human clinical trials utilizing various specific waveform formats for such treatment, including invasively-coupled, direct-current devices; capacitively-coupled, symmetric and asymmetric waveforms, and electro-magnetically coupled asymmetric waveforms. Excellent technical reviews of this field are J. A. Spadaro's Bioelectric "Stimulations of Bone Formation: Methods, Models and Mechanisms", in the Journal of Bioelectricity, Volume 1 (1), p. 99, 1982; and the Orthopedic Clinics of North America Symposium on Electrically Induced Osteogenesis, W.B. Saunders Corp. 1984.
All currently used electro-therapy therapy techniques have one or more limitations. For example, invasive techniques have the potential of increasing the risk of infection, and unpredictable and potentially long-term side effects. Capacitively-coupled systems are limited by the fact that when operated at safe voltage levels, they require electrical connection between capacitive plates and the skin in the area surrounding the fracture site. Conductive jellies are typically employed and, by their nature, do not lend themselves to long-term installation. Electromagnetically, inductively-coupled techniques have required high power consumption waveform generation devices and bulky coil configurations that compromise the patient's ability to function normally outside of the clinical environment; Representative U.S. patents describing the above devices are 4,535,775, inventors Brighton and Pollack; 4,667,809, inventor Brighton; 4,467,808, inventors Brighton and Pollack; 4,266,532, inventor Ryaby; 3,952,751, inventor Yanger; 3,893,462, inventor Manning; and 3,890,953, inventors Kraus and Viehbach.
It generally takes bone fractures, particularly non-union fractures, many weeks or months to heal, and this is true even with the aid of electro-therapy where it has been tried as an adjunct treatment in an experimental setting. Because the presently utilized electro-therapy devices are, with a few exceptions, not truly portable, if the patient is to benefit from electro-therapy, he must have ready access to a source of electric power to effect treatment. Considering the time required for a bone to heal, this constraint is particularly annoying on a day to day basis, and requires that a patient constantly interrupt his daily routine for treatment, which may in turn cause failure of the patient to comply with the required protocol. Therefore, it is apparent that it is desirable to produce a device having the effective features of the devices currently in use but lacking their undesirable features, particularly their power wasting aspects. By creating a more power-efficient electro-therapy device it is possible to considerably reduce the size of the electro-therapy machines, hence permitting the construction of a completely portable device that allows the user to go about his daily routine without being tethered to a source of electric power.
A few inventors have appreciated the practical advantages of having a portable electro-therapy device. It is important to note that portability in the art is taken to mean a device readily carried by the patient without cumbersome support aids, and particularly connotes devices less than two pounds in weight, and no larger than a conventional pocket camera. U.S. Pat. No. 4,432,361 describes a portable device that has self monitoring features thereby allowing the patient to ascertain its operational status without having to have it checked by a physician, or another person skilled in the use of the device. This invention is an improvement over that described in U.S. Pat. No. 3,842,841 which does not have the desirable self-monitoring features. Another portable electrotherapy device is described in U.S. Pat. No. 4,574,809. It shows a device suitable for integration into an orthopedic cast with a signal generator removably mounted in the cast.